O processo que usei (obrigado a Par pelo link bom):
Pré-2007
- Add your signature to AutoText
- Compose and email, filling in the header fields, so your cursor is in the body
- Right-click the toolbar and choose Customize
- Choose Autotext, then the name of your signature
- Then drag (the name) to one of your toolbars
- Rename the name with an '&' in front of the letter that you want to be the shortcut key
- You can now click on the signature button in the toolbar, or use ALT-chosenkey to insert your signature.
Observe que parece não ser possível (sem um suplemento) criar um atalho de teclado para sua assinatura no Outlook 2010.